In ODAC, we suggest you to set ScrollableCursor option of DataSet object to True, in this case TOraDataSet does not cache data on the client side but uses scrollable server cursor.
This feature is supported starting from Oracle server 9i. If you need more info pls. see ODAC help, topic TOraDataSet.OptionsDS.
You can set TOraDataSet.UniDirectional=True. ODAC will use one memory block for all records. But you cannot use such dataset with TDBGrid.